The U.S. government again is trying to clamp down on North Korea through sanctions aimed at the country's top leaders and, more specifically, the notorious Office 39, which is widely seen as an "investment bank" for North Korea's elite.

The focusing on Office 39 builds on longstanding efforts to deprive the North Korean elite of luxury goods. Sometimes known as Room 39, Office 39 is a branch of the Korean Workers' Party that raises and manages a slush fund of hard currency for Mr. Kim's family and friends.

While some of Office 39's dealings are believed to be legitimate - it exports exotic mushrooms, ginseng and seaweed, for example - the organization is suspected of being involved in the counterfeiting of American currency and drug trafficking.

The Treasury Department said Office 39 had been involved in methamphetamine distribution and the production of heroin and opium.

Office 39, which answers directly to Mr. Kim and has its headquarters not far from his villa, also procures luxury goods for the leadership. Last year, American officials said, the Italian government foiled its attempt to buy two Italian-made luxury yachts worth more than $15 million for Mr. Kim.